Caption: Volcano surveying. Alexandre Nercessian, geophysicist and seismologist, centering a GPS antenna as part of a seismic survey on the Piton de la Fournaise shield volcano. Piton de la Fournaise is one of the most active volcanoes on the planet, erupting several times a year. Since 1980 it has been consistently monitored by scientists and government surveillance facilities, in case residents need to be evacuated. Photographed on Reunion Island, Indian Ocean, in April 2007.